Magnum Exhaust Manifolds in an A Body

Do you mean the infamous Mopar Muscle article? Struggling to find a link but the one that showed like 5 or 10 HP difference between the standard manifolds and the HP manifolds?
No. I mean the Jim Laroy private dyno work. It's posted on this site somewhere, but God help you trying to find it. It wasn't in depth. All it was was basically him saying they made really no difference at all. I would trust someone like him FAR further than anyone running a magazine with sponsors.